include P16F877.inc


#DEFINE		TMR0_CONSTANT	0x50 

ARG_A_L		EQU		0x20
ARG_A_H		EQU		0x21

ARG_B_L		EQU		0x22
ARG_B_H		EQU		0x23

PROD_L		EQU		0x24
PROD_H		EQU		0x25
PROD_HH		EQU		0x26

CNT		EQU		0x7F


W_TEMP		EQU		0x7A
STATUS_TEMP	EQU		0x7B
PCLATH_TEMP 	EQU		0x7C


					org 0x00

					GOTO	START


					ORG 0x04
					
					MOVWF W_TEMP 		
					SWAPF STATUS,W 		
					CLRF STATUS 		
					MOVWF STATUS_TEMP 	
					MOVF PCLATH, W 		
					MOVWF PCLATH_TEMP 	
					CLRF PCLATH 		

					BTFSS INTCON, T0IF
					GOTO END_INTERRUPT
					MOVLW TMR0_CONSTANT
					MOVWF TMR0

					BCF	INTCON, T0IF

					BTFSS PORTB, 0
					GOTO PORTB_ZERO			
					

					BCF	PORTB, 0
					GOTO END_INTERRUPT

PORTB_ZERO			BSF	PORTB, 0
					NOP
					NOP			
			


END_INTERRUPT		MOVF PCLATH_TEMP, W 	
					MOVWF PCLATH 			
					SWAPF STATUS_TEMP,W 	
					
					MOVWF STATUS 			
					SWAPF W_TEMP,F 			
					SWAPF W_TEMP,W 			

					RETFIE

					ORG 0x100

START				MOVLW 0x10
					MOVWF CNT
					MOVLW 0x20 
					CALL CLEAR_RAM
					
					BCF	PORTB, 0
					
					BSF	STATUS, RP0
					BCF	TRISB, 0
					BCF	OPTION_REG, T0CS
					BCF	STATUS, RP0

					BCF	PORTB, 0

					MOVLW TMR0_CONSTANT
					MOVWF TMR0
					BSF	INTCON, GIE
					BSF	INTCON, T0IE
				
					MOVLW	0xFF
					MOVWF	ARG_A_L

					MOVLW	0x06
					MOVWF	ARG_B_L

					CALL	SCITANIE_8_U

					MOVLW	0xFF
					MOVWF	ARG_A_L
					MOVLW	0xFF
					MOVWF	ARG_A_H

					MOVLW	0xFF
					MOVWF	ARG_B_L
					MOVLW	0xFF
					MOVWF	ARG_B_H

					CALL	SCITANIE_16_U

LOOP				GOTO LOOP

					ORG	0x400

SCITANIE_8_U		CLRF	PROD_H
					MOVF	ARG_A_L, W
					ADDWF	ARG_B_L, W
					BTFSC	STATUS, C
					INCF	PROD_H, F
					MOVWF	PROD_L
					RETURN


SCITANIE_16_U		CLRF	PROD_HH
					CLRF	PROD_H
					MOVF	ARG_A_L, W
					ADDWF	ARG_B_L, W
					MOVWF	PROD_L
					BTFSC	STATUS, C
					INCF	PROD_H, F
					MOVF	ARG_B_H, W
					ADDWF	PROD_H, F
					BTFSC	STATUS, C
					INCF	PROD_HH, F	
					MOVF	ARG_A_H, W
					ADDWF	PROD_H, F
					BTFSC	STATUS, C
					INCF	PROD_HH, F	
					RETURN





SLUCKA				MOVWF	CNT

SLUCKA_1			NOP
					NOP
					DECFSZ	CNT, F
					GOTO	SLUCKA_1
					RETURN




CLEAR_RAM			MOVWF FSR 
NEXT 				CLRF INDF 
					INCF FSR, F 
					DECFSZ CNT, F					
					GOTO NEXT 
					RETURN


INIT_TMR0

					END